"One experience. One disappointment. One public embarrassment. One failed recognition. One, sort of, narcissistic injury ... can set someone off and set off that rage," said Dr. Gerald Shiener, M.D., of Wayne State University. "The personality of someone who would shoot at people on a freeway at random has to be someone who has a tremendous amount of rage inside them."

Meanwhile, his Twitter posts reveal he is a man with anger toward the government. Police sources tell Local 4 Casteel thinks the government is out to get him in Kentucky, where he lived for a few years. He even displayed anger at a sheriff in that state for not investigating his complaints of "privately held airplanes and military helicopters" being used to attack his property.

"They're dealing with their own feelings of powerlessness and they project it onto the people who they see are the most powerful," said Shiener.

What's going on in Casteel's mind which may have triggered the alleged shooting rampage at vehicles along roads across four Michigan counties?

"A lot of times when people do things like this, they do it for attention. If they're obscure, if they're feeling helpless, if they're feeling hopeless, if they're feeling lonely, this is a way that they can make themselves known. They can have something over on the general public because they know what's going on and no one else does," said Shiener.